In Vivo vs In Vitro: Definition, Pros and Cons

If you have read any scientific study that involves biological or medical research, then you may have encountered the terms “in vivo” and “in vitro” throughout the text. The etymological origins of in vivo and in vitro come from Latin; in vivo describes something “within a living organism” while in vitro describes something “in glass” such as a test tube or petri dish. In this article, we will define these terms and further evaluate the pros and cons of analysis using in vivo and in vitro methods with detailed examples.

An in vivo study involves testing or with living subjects such as animals, plants or whole cells. For example, clinical trials focused on assessing the safety and efficacy of an experimental drug in humans are considered in vivo studies. In vitro experiments refer to work performed with cells, tissues or other biological components that have been removed from the living organism(s) of interest. While in vivo and in vitro studies are both essential for biological research, they each present their own conveniences and challenges.¹

Before an experimental drug is studied in vivo, its mechanism of action and complexity need to be thoroughly evaluated using in vitro models. In vitro models provide a starting point for researchers to gather insights into how a cell responds to a new drug in a controlled, isolated environment.

For example, in vitro tumor models provide low-cost platforms for a pharmaceutical company to study the biological effects of experimental drug candidates against cancer cell lines. Results from these studies can inform researchers about the molecular mechanisms of each drug candidate and how these mechanisms may influence cancerous cells under defined conditions. However, these results are extremely difficult to extrapolate a clinical effect² from as they studies were not performed in an intact, living organism, where far more biological variables are in play.

Once a drug candidate demonstrates effectiveness through a series of in vitro experiments, in vivo models can be employed to advance drug development studies. These preclinical studies typically involve the use of animals to further evaluate the safety, efficacy and delivery of a drug candidate. For example, rodent models inoculated with tumor cells³ are commonly used to screen anti-tumor drug candidates that exhibited promising results throughout previously performed in vitro studies.

 

Type of Study	In vivo	In vitro
Definition	Studies “within a living organism”	Studies performed “in the glass”
Cost	Very expensive	Relatively low cost
Time	Long and extensive	Relatively fast
Example	Clinical trials and animal studies	Organ-on-a-chip, microphysiological systems, cell-based screening, diagnostic tests
Pros	More specific and reliable for observing biological effects in a test subject	Relative simplicity, species specificity, experimental control
Cons	Strict regulations and compliance standards	Physiologically limited

In vitro testing is an essential component of biological research that provides a way to study the response of human, animal or microbial cells in culture.

Organ-on-a-chip

An organ-on-a-chip is a three-dimensional, microfluidic device that combines cell culture with biomedical engineering to simulate the physiological environment of an entire organ in vitro. Today, organ-on-a-chip technologies have emerged as a promising platform for advanced drug development studies focused on studying the adsorption, distribution, metabolism and excretion properties of drug candidates. Such technologies are currently being applied to better understand the molecular mechanisms of liver, kidney, heart, lung and brain diseases.

Microphysiological system

Microphysiological systems are interconnected constructs that recapitulate the function(s) of an organ in vitro. These systems combine tissue engineering, microfabrication and biosensors to enable the organization and function of multiple tissue-specific cells over time. For example, a kidney-on-a-chip system⁴ combines functional glomerular and nephron-derived constructs to mimic a working kidney would qualify as a microphysiological system. These systems also contribute to the technological trends behind advances in drug discovery at the preclinical stage.

Humans and animals share a lot of anatomical and physiological features with comparable functions. Consequently, animal testing and clinical trials make up the bedrock of in vivo studies involving drug discovery.

Animal models (preclinical)

Before a drug candidate is tested in human subjects, it must undergo rigorous animal testing to further evaluate its toxicity, metabolism and overall efficacy. Vertebrate animal models such as rodents, primates, dogs and rabbits are commonly used for preclinical in vivo studies. Mice are the most used vertebrate species due to a combination of factors such as size, ease of handling, fast reproduction and low cost. Mice also share 95% of their genes with humans,⁵ which makes them very attractive models for studying human diseases. These factors contribute to their usefulness when it comes to evaluating the safety and efficacy of drug candidates at the preclinical stage.

Human trials (clinical)

Once a drug candidate has demonstrated sufficient efficacy and safety during animal studies, human studies may commence. Researchers at this stage are interested in assessing whether a treatment is safe and effective for its intended population of subjects. Humans who partake in a clinical trial will be closely monitored to evaluate the drug metabolism and pharmacokinetic qualities of the experimental therapy over time. These trials need to perform such analyses with continued monitoring afterward so that drug candidates can be thoroughly evaluated to be safe and effective.